1. Field of the Invention
The present invention relates to an optical waveguide and a manufacturing method thereof, and more particularly, to a hybrid optical waveguide having reduced optical travel loss and a small waveguide using different waveguide component materials in a linear section thereof and a curved section thereof, and to a manufacturing method thereof.
2. Description of the Related Art
In general, when an optical waveguide is constructed, a difference in refractive indices or specific refraction between a core and a cladding, and the size and curvature of a waveguide crosssection are parameters which affect each other. A curved section in an optical waveguide must be formed of an optical material having a relatively large refractive index, in order to reduce the travel loss of an optical signal passing through the curved section. When an optical waveguide is formed of a material having a relatively large refractive index in consideration of loss in the curved section, the size of a waveguide cross-section suitable for the refractive index is reduced in a linear section without curvature, so that an optical fiber coupling loss is increased upon connection of the waveguide to an optical fiber. On the contrary, if the optical waveguide is fabricated of a material having a relatively small refractive index suitable for the linear section, the travel loss of an optical signal increases in the curved section.
An optical waveguide includes a planar substrate, a lower cladding, an upper cladding, and a waveguide formed of an optical polymer having a specific refractive index. The cross-section of the waveguide must have a specific cross-sectional area in accordance with the specific refractive index to minimize the travel losses of an optical signal. However, the travel losses of the optical signal is significantly higher in a curved section of the waveguide, i.e., in a portion including a curvature, so that the radius of curvature must be large. Another optical waveguide includes a planar substrate, a lower cladding, and a waveguide formed of an optical polymer having a specific refractive index. The cross-section of the waveguide must be of a specific cross-sectional area in accordance with the specific refractive index. Because of the large refractive index, the travel losses of an optical signal in a curved section decrease even when the radius of curvature of the curved section is small whereas the travel losses in a linear section increases. Also, the loss for coupling of a waveguide to an optical cable may be increased because the cross-section of the waveguide must be small.
When such optical waveguides having a curved section is formed of a polymer using an equal specific refractive index, losses of the optical signal must be traded-off with the size of the waveguide. With higher levels of integration of a device including the optical waveguide, and with an increase in the necessity for a waveguide having a curvature, the necessity for solving the above problem increases.